Know Your Friends

Galerucella
calmariensis and G. pusilla are members of the
leaf-feeding family of beetles called Chrysomelidae. Native to
Europe and Asia, these beetles are currently being used to help
control purple loosestrife in the United States and Canada.

Both beetles look very similar and have nearly
identical life cycles. They range from 3-6 mm in length and are
about half as wide as they are long. Coloration is light brown or
tan, sometimes with a dark stripe on each side of the insect when
viewed from the top. It is not possible to differentiate between
the two species in the field due to variability in key
characteristics.

In spring (late April or May) overwintering
adults emerge from soil and litter below old purple loosestrife
plants to feed for several days on new foliage and then begin to
reproduce. After mating, females lay eggs in masses of 2 to as
many as 20 eggs per grouping, which may be placed low on the
stem, at leaf axils, or on leaves. The egg-laying period occurs
from mid-May to mid-July with the peak in May and June. An
individual female may lay up to 500 eggs during this period.
Larvae emerge from eggs in 7-10 days and feed on tissues of
developing shoots and leaves. When larvae commence feeding adults
may disperse, migrating to other nearby plants. Larvae feed for
about three weeks, going through several instars before moving
down into the soil or plant litter to pupate. Where water levels
are higher, larvae may pupate inside the stem by burrowing into
aerenchyma tissue (plant tissue containing cells composed
primarily of air giving many aquatic plants buoyancy). Upon
emergence the new adults harden in seven to ten days, then feed
until moving into the litter or soil below to overwinter. This
period of emergence occurs typically from July to September. The
total maturation time from egg to adult is approximately 30-40
days.

The two Galerucella species inhabit
loosestrife throughout the plant's natural range in Europe and
Asia where, along with other natural enemies, they help keep
purple loosestrife in check. Both species will lay eggs only on
purple loosestrife and are specific feeders as well. The Galerucella
beetles cause significant damage to purple loosestrife. Adults
inflict a shothole feeding pattern eating small (1-2 mm) holes
through foliage. Newly hatched larvae feed in growing shoot tips,
killing them. Larger larvae produce a windowpane feeding pattern
on the leaves, eating the softer tissues and leaving the tougher,
less digestible veins.

Larval damage to flower and shoot buds reduces
plant growth and inhibits flowering. Adult and larval leaf damage
greatly reduces the photosynthetic capability of purple
loosestrife, possibly leading to reduced starch stores in the
roots which can result in winter plant mortality. Photosynthetic
inhibition results in reduced stem height and root length, both
essential to overall plant vigor. The resultant weakening and/or
death of the loosestrife plants provides an opportunity for
previously out-competed native plant species such as cattails,
grasses, and sedges to return.

The beetles can fly between plants or plant
clusters and both larvae and adults float, allowing current or
wind to move them to nearby plants. Unfortunately, long-term
standing water may be detrimental to Galerucella's
development since pupation is difficult under these conditions.

It is expected that the establishment of
permanent stable populations of G. calmariensis and G.
pusilla on purple loosestrife will reduce this plant to
levels that may be tolerated by North American wetland
ecosystems.